The SPS as a Damping Ring Test Facility

July 10th, 2013

F. Antoniou, R. Corsini, L. Evans and

Y. Papaphilippou

Test Facility for DR R&D

Y.P., 10/07/2013 SPS DR Test facility 2

Damping rings (DRs) target low emittances in all 3 dimensions for relatively high bunch charge

Dominated by collective effects Technology of systems driven

by design choices for reducing these effects

Experimental program was set-up to test most challenging systems

Ideal future scenario: use existing ring as test facility (TF) for DR R&D, for testing components and interdependencies in similar beam conditions

Existing or future light source storage rings would be ideal for these tests

Obvious drawback the beam time availability for experiments

Unconventional approach: use SPS as DR TF

PARAMETER 2 GHz 1 GHz

Energy [GeV] 2.86

Circumference [m] 427.5

Bunch population [109] 4.1

Wiggler field [T] 2.5

Wiggler length [m] 2.0

Wiggler period [cm] 5

Damping times [ms] (2.0,2.0,1.0)

Momentum compaction [10-4] 1.3

Energy loss/turn [MeV] 4.0

Repetition rate [Hz] 50

number of bunches/train 312 156

number of trains 1 2

Horizontal normalized emittance [nm.rad] 472 456

Vertical normalized emittance [nm.rad] 4.8 4.8

Energy spread [%] 0.1 0.1

Bunch length [mm] 1.6 1.8

Longitudinal normalized emittance [keV.m] 5.3 6.0

RF voltage [MV] 4.5 5.1

Bunch spacing [ns] 0.5 1

RF acceptance [%] 1.0 2.4

SPS

Reviving old ideas, when SPS was running also as a LEP injector

More recent ones, serving as e+ DR for LHeC

Evans and Schmidt, 1988

Papaphilippou 2011

Y.P., 10/07/2013 SPS DR Test facility

SPS low emittance optics SPS is an all FODO cell lattice (6

sextants), with missing dipole Usually tuned to 90 deg. phase

advance for fixed target beams (Q26) and since 2012 to 67.5 deg (Q20) for LHC beams

Move horizontal phase advance to 135(3π/4) deg. (Q40)

Normalized emittance with nominal optics @ 3.5GeV of 23.5μm drops to 9μm (1.3nm geometrical) Mainly due to dispersion decrease Almost the normalized emittance

of ILC damping rings Damping times of 9s Natural chromaticities of -71,-39

(from -20,-27)

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Parameterisation Use classical formulas for horizontal equilibrium emittance,

damping time, energy spread and bunch length, in presence of wigglers (CLIC DR prototype parameters)

Assume SPS bending characteristics and placing of wigglers at lowest horizontal beta function location (~9-10m) and almost zero dispersion (close to defocusing quads of dispersion suppressor)

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Emittance Energy and damping time can be parameterised with

equilibrium emittance, for different wiggler lengths Ultra-low emittance achieved in energy range of 2 to

5GeV

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For reaching emittances below the CLIC target of 500nm (i.e. from 130 to 50pm geometrical in that energy range), a few meters of damping wigglers should be used

Wiggler Length

It is only possible to reach ultra-low equilibrium emittance and very fast damping time, when a large number of wigglers is included

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Energy loss per turn Energy loss per turn proportional to energy and inversely

proportional to damping time In particular for 3.5GeV and 10m wigglers, ~0.7MeV, i.e. enough RF

voltage available (~7MV) Note that for SPS during the LEP era, extra cavities were installed

providing 30MV

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Energy spread Energy spread depends weakly on damping time for lower energies Higher energies show a rapid change with damping time Generally, values lie between 0.1 and 0.2% In particular for 3.5GeV, energy spread of ~0.15%

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Bunch length Bunch length has very similar behaviour as energy

spread for fixed voltage (5MV in this example) In particular for 3.5GeV, bunch length of 16mm

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GeometricalAcceptance

11Y.P., 10/07/2013

Assuming CLIC pre-damping ring beam parameters

Wiggler gap needed of the order of 3 cm (1.3cm for CLIC prototype)

SPS DR Test facility

Intrabeam Scattering

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Scaling of the blow-up due to IBS in the horizontal plane with the bunch population, @ 3.5GeV for different total wiggler length (thus damping times and zero current emittance)

IBS

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Scaling of the IBS blow-up in the horizontal plane (blue) and the zero current horizontal emittance (green) with energy For a total wiggler length

of 10 m and for the CLIC bunch current Nb=4.07E9

Minimum at around 5GeV but still a factor of 2 blow up

Parameter Choice

Interesting parameters for one 2m-wiggler (CLIC prototype) or five (10m total length), crossing the CLIC and ILC target emittances, at 2.6, 3.5, 5 and 6.6 GeV

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Tentative parameters

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Parameter [Unit]

Lw=0m

Lw=2m

Lw=10m

Lw=2m

Lw=10m

Energy [GeV] 3.5 2.6 3.5 5 6.8Hor. Norm. emit. [nm]

8800 480 5600

Damping time (x,y) [sec]

9 1.46 0.22 0.64 0.11

Bunch length [mm]

3.6 11.5 16.1 20.5 32.5

Energy spread [%] 0.011 0.13 0.15 0.16 0.20Energy loss/turn [MeV]

0.02 0.08 0.72 0.36 2.8

Bunches/pulse <=9221Bunch spacing [ns]

5

Repetition rate [Hz]

0.83

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EP Injector complex

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Need to revive a “LEP-like” injector complex

Pre-injector includes and e/p linac at a few hundreds MeV (LIL at LEP), and accumulator (EPA for LEP)

It should be transferred through PS to SPS

Transfer line for positrons exists (TT10) but for electrons (TT70) completely dismantled

Further studies

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Consideration for the injector complex (CTF3?) Parameters for the PS at different energies

considered Transfer-line and injection/extraction

elements Complete parameter set for SPS including

DA and coupling simulations, collective effects and synchrotron radiation absorption

Test the new optics in the SPS with protons (2015)

Establish synergies with different projects (LHeC, TLEP, AWAKE,…)

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ELectron Positr

on Injector Design Study

ELPIDES